This invention concerns dimension control of a rolling material in a continuous rolling machine having a hole roll, for example, a bar steel mill and a wire mill.
An example of the structure of a continuous rolling machine having a hole roll is shown in FIG. 1. FIG. 1 shows a continuous rolling machine comprising i mill stands, including a first mill stand 1, a second mill stand 2, an (i-1)th mill stand 3 and an ith mill stand 4, and a rolling material 5 successively rolled through these mill stands.
In the continuous rolling machine of this kind, i.e. a vertical-horizontal (VH) mill, horizontal mills (odd-numbered mills in FIG. 1) and vertical mills (even-numbered mills in FIG. 1) are usually arranged alternately. For instance, the (i-1)th mill stand 3 is a vertical mill performing the rolling in the direction X in which bi-1 represents the lateral dimension and hi-1 represents the vertical dimension at the exit of the (i-1)th mill stand 3. While on the other hand, the ith mill stand 4 is a horizontal mill performing the rolling in the direction Y in which bi represents the lateral dimension and hi represents the vertical dimension at the exit of the ith mill stand 4.
Conventional continuous rolling machines such as a bar steel mill and a wire mill include, for example, those adapted to control the speed of a motor that drives the (i-1)th mill stand 3 so that the amount of the loop between the ith mill stand 4 and the (i-1)th mill stand 3 may be rendered constant, or those adapted to control the rolling position by detecting the change of the vertical dimension at the exit of the mill by mill rigidity control devices (BISRA control devices) based on the rolling load detected by load cells. As used herein and in the appended claims, "rolling position" refers to the distance between opposed rollers in a particular mill stand. However, machines employing dynamic control have so far been unknown for a number of reasons, for instance since there have been no severe requirements for the dimensions of products, and since mill elongation due to the change in the load during rolling is small (which makes the dimensional accuracy of the products better since the effect of transferring the change at the inlet of the rolling material to the exit is decreased).
Accordingly, since no dynamic control has been provided in the conventional control system for compensating the change in the dimension of the rolling material relative to changes in the temperature or the like, the dimensional accuracy is sometimes unsatisfactory.